Development of prediction technology of two-phase flow dynamics under earthquake acceleration

Abstract

In this study, to develop the predictive technology of two-phase flow dynamics under earthquake acceleration, a detailed two-phase flow simulation code with an advanced interface tracking method TPFIT was expanded to perform two-phase flow simulations under seismic conditions. In the expansion of the TPFIT, the oscillating acceleration attributed to the earthquake motion was introduced into the momentum equation of the two-phase flow as body force. Moreover, to simulate fluctuation of the flow rate and a shear force on a pipe wall, time dependent boundary conditions can be added in the numerical simulations. The bubbly flow in a horizontal pipe excited by oscillation acceleration and under the fluctuation of the liquid flow was simulated by using the modified TPFIT. Furthermore, predicted velocity distribution around the bubbles and shapes of bubbles were compared with measured results under flow rate fluctuation and structure vibration. In the results of numerical simulation, periodical change of shapes of bubbles was observed. In addition, velocity distribution around bubbles also changed in accordance with flow rate fluctuation or structure vibration. Predicted results almost agreed with measured results. In the results, it was confirmed that the modified TPFIT can predict time dependent velocity distribution around the bubbles and shapes of bubbles qualitatively. The main cause of bubble deformation observed from the measured and predicted results is large shear stress at the lower part of the bubble, and this large shear stress is induced by the velocity difference between the liquid phase and bubble. Moreover, by using the predicted results, we discussed about the difference between both effects of flow rate fluctuation and structure vibration on two-phase flow. In the results, bubble acceleration of the structure vibration case was larger than that of the flow rate fluctuation case. Finally, it was concluded that unsteady shear stress induced by vibration of the pipe wall was one of the main driving forces of bubble motion in structure vibration case.

Keywords

• earthquake acceleration
• two-phase flow
• interface tracking method
• computational fluid dynamics
• tpfit
• oscillating flow